Steam reforming utilizing iron oxide catalyst

ABSTRACT

High activity steam reforming iron oxide catalysts are described. Such catalysts can be unsupported utilizing at least 90% by weight iron oxide and various modifiers (Al 2  O 3 , K 2  O, CaO, SiO 2 ) or unmodified and supported on such things as alumina, CaO impregnated alumina, and lanthanum stabilized alumina. When used in steam reformers such as autothermal and tubular steam reformers, these catalysts demonstrate much improved resistance to carbon plugging.

This is a division of application Ser. No. 372,252 filed on Apr. 26,1982 now U.S. Pat. No. 4,451,578.

DESCRIPTION

1. Technical Field

The field of art to which this invention pertains is catalytic reformingof gaseous and/or liquid hydrocarbons utilizing the injection of steamto produce hydrogen.

2. Background Art

In the production of hydrogen, it is well known in the art to treathydrocarbon material with a catalyst at high temperatures in thepresence of steam. The hydrocarbon materials generally used are naturalgas and naphtha which have been desulfurized to 0.1 part per million(ppm, by weight) sulfur. Hydrogen, carbon monoxide and carbon dioxideare the products of the reaction. These products are often cooled andpassed over a shift conversion catalyst where the carbon monoxide isfurther reacted with steam to produce additional hydrogen and carbondioxide.

Hydrogen generators and especially hydrogen generators for fuel cellpowerplants may be required to operate with heavier fuels and, in thefuture, coal derived liquids. These heavier distillate fuels cannotreadily be desulfurized to the 0.1 ppm sulfur level that is required forthe conventional steam reforming process. Direct reforming of heavierfuels without desulfurization require higher temperatures to overcomethe reduction in catalytic activity in the presence of sulfur. When thecommercially available nickel steam reforming catalysts are used in thisfashion, carbon deposition and reactor plugging occur and reactoroperation cannot be sustained. The problem of carbon formation withconventional nickel catalysts can be overcome by adding air or oxygen tothe hydrocarbon/steam fuel mixture. At oxygen to carbon ratios (O₂ /C)equal to or greater than 0.42-0.46 carbon formation is eliminated with a1380° F. (738° C.) preheat. In order to maximize the hydrogen productionit is desirable to lower the oxygen to carbon ratio below 0.42. Forexample, for fuel cell powerplant applications, O₂ /C in the range of0.35 are desirable.

Accordingly, what is needed in this art is a catalyst which is lesssusceptible to carbon formation and which in an autothermal reformerallows operation at reduced O₂ /C ratios.

DISCLOSURE OF INVENTION

The present invention is directed to a catalyst specifically adapted foruse in autothermal and tubular steam reforming systems whichsubstantially eliminates carbon plugging in such reforming systems andallows autothermal reformers to operate at reduced O₂ /C ratios withheavier distillate hydrocarbons such as No. 2 fuel oil. Such catalystscomprise stabilized iron oxide containing at least 90% by weight ironoxide and iron oxide supported on an alumina carrier. The alumina canoptionally be lanthanum stabilized or calcium oxide impregnated.

Another aspect of the invention includes an autothermal reformingprocess utilizing the catalyst system according to the presentinvention.

Another aspect of this invention includes a tubular steam reformingprocess utilizing the catalyst system according to the presentinvention.

The foregoing, and other features and advantages of the presentinvention, will become more apparent from the following description andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows regions of carbon-free steam reforming operation forvarious catalysts as a function of oxygen to fuel carbon ratios andreaction temperature.

FIG. 2 shows activity of catalyst material according to the presentinvention as a function of temperature.

BEST MODE FOR CARRYING OUT THE INVENTION

The iron oxide catalysts according to the present invention can compriseeither ferrous oxide or ferric oxide and in general (note the examplesbelow) comprise a mixture of the two. If unsupported, the iron oxidecontains promoters such as alumina, potassium oxide, calcium oxide andsilicon dioxide in relatively small amounts, for example, up to about 2%by weight which can be added during catalyst preparation. In suchinstances, the iron oxide (FeO and Fe₂ O₃) comprises at least 90% byweight of the catalyst. The supported iron oxide is generallyimpregnated into the alumina substrate out of aqueous solution. Thesupported iron oxide comprises from about 10% to about 90% by weight ofthe catalyst plus substrate according to the present invention, andpreferably comprises about 20% to about 30% by weight. Although thesupported iron oxide can contain promoters or modifiers, typically itdoes not.

As the substrate material, either Al₂ O₃, a lanthanum stabilized aluminaor a calcium oxide impregnated alumina can be used. Although the Al₂ O₃pellets are sized depending on reactor size and other system variables,they are typically about 0.125 inch (0.318 cm) in diameter with anaverage length of about 0.14 inch (0.356 cm) and are availablecommercially from Harshaw Chemical Co., Cleveland, Ohio (designatedAl-4104E). The lanthanum stabilized alumina substrate is a commerciallyavailable catalyst support material available from W. R. Grace & Co.(e.g. Grace SRDX-1/79-1). The calcium oxide containing alumina isprepared by impregnating the alumina with a solution (preferablyaqueous) of a calcium salt (preferably calcium nitrate) followed bydrying to remove the solvent, and calcining in air to oxidize thedeposited salt to calcium oxide. Calcining temperatures may varydepending on the particular salt used, but generally temperatures ofabout 1850° F. (1010° C.) are used, e.g. for calcium nitrate. Enoughcalcium salt is deposited on the support material such that aftercalcining about 10% to about 35% calcium is present in the supportmaterial, and preferably about 15% by weight.

The iron oxide catalyst material according to the present invention isdeposited on the substrate material by any conventional method in thisart, and as stated above, preferably out of aqueous solution. Metalsalts and typically the nitrates are dissolved in either aqueous ororganic solvents and dried on the substrate. The deposited salts arethen calcined to form the oxides.

EXAMPLE 1

Steam reforming catalysts according to the present invention wereprepared as follows: 5 grams of extruded Al₂ O₃ pellets having adiameter of 0.125 inch (0.318 cm) and an average length of 0.14 inch(0.356 cm) (available from Harshaw Chemical Co., Cleveland, Ohiodesignated as Al-4104E) were impregnated with 7.5 ml of an aqueoussolution which contained 1.2 gm Fe(NO₃)₃.9H₂ O per ml of solution. Theimpregnated material was then placed in an ultrasonic blender for 5minutes. The material was removed from the ultrasonic blender, allowedto stand for 1/2 hour at room temperature, dried for 11/2 hours at 300°F. (149° C.), and calcined overnight at 1860° F. (1016° C.).

EXAMPLE 2

Iron oxide on lanthanum stabilized alumina was prepared as follows: 1713grams of Fe(NO₃)₃.9H₂ O were dissolved in 212 ml of water. This solutionwas used to impregnate pellets of a lanthanum stabilized aluminasubstrate, commercially available from W. R. Grace Corporation (DavisonDivision) under the designation SRDX-1/79-1. The pellets were sizedsimilar to those of Example 1. The mixture was placed in an ultrasonicblender for 5 minutes, allowed to stand for 30 minutes and the excesssolution was decanted. The catalyst was dried at 270° F. (132° C.) for3.5 hours and then calcined at 1502° F. (817° C.) for 16 hours. Thefinished product weighed 980 grams.

EXAMPLE 3

A steam reforming catalyst of iron oxide on CaO containing Al₂ O₃ wasprepared as follows:

A solution consisting of 600 grams of Ca(NO₃)₂.4H₂ O dissolved in 177 mlof H₂ O was used to impregnate 365 grams of Al₂ O₃ pellets as describedin Example 1 (Harshaw Al-4104E). The impregnated material was placed inan ultrasonic blender for 5 minutes and then allowed to stand for 30minutes. The excess solution was then decanted, dried at 300° F. (149°C.) for 11/2 hours and calcined at 1850° F. (1010° C.) for 16 hours.This product weighed 426 grams. This material was then impregnated witha solution consisting of 425 grams of Fe(NO₃)₃.9H₂ O dissolved in 47 mlof H₂ O. The material was placed in an ultrasonic blender for 5 minutes,allowed to stand for 30 minutes and then excess solution was decanted.The catalyst was dried at 290° F. (143° C.) for 3 hours and calcined at1830° F. (999° C.) for 16 hours. The impregnating with Fe(NO₃)₃.9H₂ O,blending, drying and calcining was then repeated.

EXAMPLE 4

An unsupported, stabilized iron oxide catalyst designed for ammoniasynthesis was purchased from Katalco Corporation of Oak Brook, Ill. Thismaterial was purchased with the designation Katalco 35-4 and had thefollowing chemical composition (percent by weight):

    ______________________________________                                        FeO                  24.5                                                     Fe.sub.2 O.sub.3     69.1                                                     Free Fe              nil                                                      Total Fe             93.6                                                     Al.sub.2 O.sub.3     2.5                                                      K.sub.2 O            0.8                                                      CaO                  2.0                                                      SiO.sub.2            0.4                                                      P                    Trace                                                    S as SO.sub.3        Trace                                                    Chloride             <10 ppm                                                  Fe/Fe                0.41                                                     Other minor impurities                                                                             Traces V and Ti                                          ______________________________________                                    

An example of the improved performance of catalysts according to thepresent invention is shown in FIG. 1 where A is a commercial nickelcatalyst (25% by weight nickel on an α-alumina support material); B isthe CaO on Al₂ O₃ of Example 3; and C is iron oxide on CaO impregnatedAl₂ O₃ of Example 3 and D the unsupported catalyst of Example 4.

Testing was performed in an autothermal reformer 2 inches (5.08 cm) indiameter and about 24 inches (60.96 cm) long. Heat was provided byinternal combustion of the fuel and air. No. 2 fuel oil was used as thefuel. It can be seen that not only is there a reduction in carbonformation on the catalyst material using the No. 2 fuel oil, but theoxygen to fuel level can be kept significantly lower than thecoventional nickel catalysts and even other oxides resulting in improvedquality of hydrogen produced and increase in reforming efficiency.

In the Table, another demonstration of the improved performancecatalysts of the present invention provide over conventional nickelcatalysts is shown. Testing was performed under tubular steam reformingconditions using an electrically heated tubular steam reformer 1.25inches (3.18 cm) in diameter and 5 feet (152.4 cm) long, with an inlettemperature of about 950° F. (510° C.) and an outlet temperature ofabout 1675° F. (913° C.) using No. 2 fuel oil as the fuel. Pressure drop(indicating a decrease in efficiency) was measured as a function of timeas indicated.

                  TABLE                                                           ______________________________________                                                        Increase in the                                               Catalyst        Pressure Drop                                                                              Time - Hours                                     ______________________________________                                        Nickel on Calcium                                                                             9 psig        15 hours                                        Aluminate                                                                     Iron oxide on   0 psig       100 hours                                        CaO/Al.sub.2 O.sub.3                                                          Iron oxide on   0 psig       100 hours                                        Lanthanum Stabilized                                                          Alumina                                                                       ______________________________________                                    

FIG. 2 also shows the improved performance characteristics of catalystsaccording to the present invention where D is the unsupported iron oxideof Example 4; C is the iron oxide on CaO impregnated alumina of Example3; E is the iron oxide on untreated alumina; and F is the iron oxide onlanthanum stabilized alumina of Example 2.

The reactants were steam reformed in an isothermal tubular steammicroreformer 0.305 inch (0.775 cm) inner diameter containing 1 inch(2.54 cm) in length, or 0.5 gram, of catalyst material. Ethanecontaining 2,225 parts per million by weight H₂ S (at about 1 atmospherepressure) was used as the fuel.

In the Figure, the data for catalysts is shown on a conventionalArrhenius Graph. In this graph, the reaction rate constant (k) isplotted against the reciprocal of the absolute test temperature. Thereaction rate constant (k) (synonymous with activity) is defined by thepseudo-first order rate equation: ##EQU1##

In previous testing with Al₂ O₃ pellets (Harshaw Al-4104E) visualinspection of the microreactor catalyst showed carbon formation in thecatalyst bed. However, addition of iron oxide according to the presentinvention to this same alumina substantially eliminated such carbonformation. With the Al₂ O₃ pellets the carbon deposited was ofsufficient magnitude to form a matrix which encapsulated the aluminaparticles and resulted in a large aggregate of many alumina particlesencased in carbon. When the Al₂ O₃ pellets contained iron oxide as inthe Examples, no carbon was found in the catalyst bed. Visual inspectionof the (Katalco 35-4) iron oxide on the lanthanum stabilized alumina andiron oxide on the CaO impregnated Al₂ O₃ also showed no carbonformation.

Types of reformers in which the catalysts according to the presentinvention demonstrate the improved resistance to carbon formation aretubular reformers, autothermal reformers, adiabatic reformers and cyclicreformers. The primary difference between these reformers is the mannerin which heat is supplied for the endothermic reforming reaction. In thetubular reformer, the heat is supplied through the walls of a cylinderto the catalyst material. Note commonly assigned U.S. Pat. No.4,098,589, the disclosure of which is incorporated by reference. In theautothermal reformer, the heat is supplied to the catalyst bed directlyby the heated gases entering and combusting in the reformer. Notecommonly assigned U.S. Pat. No. 3,967,507, the disclosure of which isincorporated by reference.

In the cyclic reformer, a plurality of reformers are operatedsimultaneously with one set of reformers operating under a combustionphase (reacting fuel and air) to provide the necessary heat for thehydrogen production phase and the other set of reformers operating underthe hydrogen production phase (reacting hydrocarbon and steam), with aswitching of phases when the temperature of the reformers in thehydrocarbon production phase drops below that necessary to sustainhydrogen production. Note commonly assigned U.S. Pat. No. 4,293,315, thedisclosure of which is incorporated by reference. In the adiabaticreformer, a conventional heat exchanger is utilized to supply therequisite heat to the steam and hydrocarbon prior to passage into thesteam reformer.

As stated above, in the autothermal reforming process fuel, steam andpreheated air are mixed and passed over the catalyst bed. The air isadded to the reactants to raise the temperature of the reactants andsupply the endothermic heat for reaction. In order to operateefficiently, the quantity of air added must be kept to a minimum. Arepresentative ratio of oxygen to carbon in the hydrocarbon is 0.35 to 1at 1360° F. (738° C.) (note the Figure) significantly lower than the0.42-0.46 using commercial nickel catalysts. This tends to lowerreaction temperature and increase the activity of the catalysts used inthis environment. At operating temperatures, conventional steamreforming catalysts such as nickel on alpha alumina are deficient inactivity.

While the iron oxide catalysts according to the present invention can beused alone, a particularly attractive arrangement for the autothermalreformer includes the use of only an inlet portion of iron oxidecatalyst according to the present invention in such reformer. In thisinlet region, all the oxygen reacts with the hydrocarbon andtemperatures increase very rapidly. Downstream of this region, thereactor is loaded with high activity nickel or rhodium catalysts asdescribed in commonly assigned copending application Ser. No. 333,841,filed Dec. 23, 1981, the disclosure of which is incorporated byreference. In this latter region, hydrocarbons and reactionintermediates react with steam. Due to the endothermic nature of thereaction with steam, temperatures drop, and it is important to have ahigh activity catalyst in this region. Typical ratios for suchmulti-catalyst system are one-third of the reactor length comprising theiron oxide catalyst of the present invention and two-thirds of thereactor length comprising the high activity nickel or rhodium describedabove. The use of such a multiple catalyst system allows greaterflexibility in the maximum allowable reactor temperature and the methodof introducing the air into the reactor.

Although the present invention has been described specifically in termsof autothermal and tubular steam reformers, it would be obvious to oneskilled in this art that such systems could be used in the other typesof steam reformers mentioned above as well. Furthermore, although theentire range of useful fuels has not been run through the catalystsystems according to the present invention, based on the reactionsinvolved, it is felt that natural gas or any hydrocarbon fuel with aboiling point as high as No. 2 fuel oil is useful with the catalyst ofthe present invention. Furthermore, the catalysts according to thepresent invention are useful with any system where carbon formation is aproblem such as oxidation reactions, gasification of heavy fuels, steamcracking as in ethylene production, etc. It should also be noted thatwhile the iron oxide catalyst systems have been described as preferablysupported, one may use such systems unsupported (e.g. the Katalco 35-4iron oxide catalyst) in steam reforming processes according to thepresent invention if one is willing to suffer the lessened performanceshown above (e.g. note FIG. 2). And while this invention has beendescribed in terms of alumina, calcium oxide impregnated alumina andlanthanum stabilized alumina catalyst carrier material, it is possiblethat similar improved results are obtainable with other promoted aluminacarrier material such as magnesium oxide, magnesia and titania promotersor magnesia and titania carrier material containing no alumina as well.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

We claim:
 1. In an autothermal steam reforming process including passinga mixture of hydrocarbon fuel, steam and preheated air over a catalystbed to form hydrogen, wherein the improvement comprises using as thecatalyst material iron oxide deposited on a lanthanum stabilized aluminasubstrate, the iron oxied comprising about 20% to about 30% by weight,to substantially eliminate carbon plugging in such reforming systems andallow operation of the reforming process at reduced oxygen to carbonratios with heavier distillate hydrocarbons such as No. 2 fuel oil. 2.In a tubular steam reforming process including passing a mixture ofhydrocarbon fuel, steam and air over a catalyst bed contained in acylindrical vessel and supplying heat to the catalyst bed through thevessel walls, wherein the improvement comprises using as the catalystmaterial iron oxide deposited on a lanthanum stabilized aluminasubstrate, the iron oxide comprising about 20% to about 30% by weight,to substatially eliminate carbon plugging in such reforming system andallow operation of the reforming process at reduced oxygen to carbonratios with heavier distillate hydrocarbons such as No. 2 fuel oil. 3.The process of claim 1 where the alumina substrate is calcium oxideimpregnated.
 4. The process of claim 2 where the alumina substrate iscalcium oxide impregnated.
 5. The process of claims 1 or 2 where thesubstrate is in the form of pellets.